Pressure



sEARcnRum 0R RE 229226 FIP8308 Dec. 1, 1942. s. E. BUCKLEY METHOD FOR RECOVERING LIQUID FROM GASES Original Filed March 31, 1939 4 Sheets-Sheet 1 S LIQUID GAL/NC? GA! X0 m mu MW um GIGS DEVI POINT CURVE 06L 1 s. a BUCKLEY I A t 1 METHOD FOR RECOVERING LIQUIDS FROM 'GASES Fnd March 51, '1939 4 Sheets-Sheet 2 GALzPER Mm: 7

GAS

PRESSURE: Les/so. IN; GA.

cms uqum: o GAL. PER mar. GAS

PRESSURE LBS/SQJMGA.

FIG 4 Dec. 1, 1942.

S. E. BUCKLEY Original Filed larch 31, 1939 4 Shouts-Shut 3 4 FTC-.5-

1942- s. r; BUCKLEY IETHOD FOR RECOVERING LIQUID FRO" GASES Original Filed llarch 31, 1939 4 Sheets-Sheet 4 Reissues! Dec. 1, 1942 fltuartllluekl ll 'r r carton, y

assignments, to Tidewater Oil Company, Tulsa, 0th.. and Seaboard Oil Company or Delaware, Dallas, Team, both corporations oi Delaware- Original No. c.2423, dated May 1:, 1941. serial No. ceases, March :1, mo. Application for reissue May 2:, 1942, serial No. 444.169

5 Claims. (CI. 82-1755) The present invention is directed to a method ior recovering normally liquid constituents from gases. More specifically, this invention is directed to the recovery at gasoline from natural gas and irom refinery gases 01 a composition similar to that at natural gas.

Natural hydrocarbon gas from diii'erent sources contains varying amounts oi normally liquid hydrocarbons which are desirable constituents of gasoline. These gases are usually produced at high pressures ranging upwardly oi 1000 pounds per square inch. At these pressures and 'at ordinary temperatures certain phase laws operate which render recovery oi the'.normally liquid constituents by the conventional scrubbing methods dimcult or impractical, since, under these condltions,-although the gas may contain a substantial percentage of normally liquid compcnents, the gas as a whole has the characteristics of a dry gas. Accordingly, it has been the astom to reduce the gas pressure considerably, so as to make possible a substantial recovery at normally liquid constituents by scrubbing.

0n the other hand, it is irequently desirable torecoverthenormallydrygasatahighpressure, because this gas is frequently used ior repressuring the producing substrate. Moreover, it is desirable irom an economic point oi view to conserve the pressure energy oi this gas for useful purposes whether or not it is to be used for repressuring. Whenthegasistobeusedior repressuring, precompression oi it before introduction into the producing substrate is necessary and ior this reason the important factor to be considered is that the cost of compressing a gas to a certain ilnal pressure multiplies rapidly as the initial pressure oi the gas decreases. Accordingly. it is desirable to recover the normal liquid constituents from the gas with as small a reduction oi pressure or the gas as is possible, consistent with an economic recovery of liquid constituents. That is to Bay. a balance must be struck between the cost of recompressing the gas and the value of the recovered liquid constituents.

The principal object of the present invention is the provision 01' a method for recovering normally liquid constituents irom gases under high an additional object is a provision oi the method 01' thecharact'er described which can be car- -rled out with simplified equipment and with lower operating and maintenance cost with a maximth um utilization of the energy contained in Another object oi.the present invention is. the provision of a method oi the character described in which is included a step oi drying the gas so that the equipment wfll not become plugged with ice and solid hydrates.

Still another object at the present invention is the provision oi a method oi the character described in which the pressure on the liquid condensate is utilized to produce reirigeration inthe further stabilization of this liquid con densate.

A further object oi the present invention is the provision oi a method oi the character described in which the normally dry gas which is dissolved in the liquid condensate recovered. is

removed from this condensate and subjected to a treatment tor the recovery therefrom oi condensahle constituents which it carries oil from the condensate. i

Further objects and advantages oi the present invention will appear irom the iollowing detailed description oi the accompanying drawings inwhich Fig. l is a iront elevation, partly in section, oi one type oi apparatus suitable tor the practice oi the method of the present invention,

Fig. 2 is a phase diagram, graphically presenting the phase relations oi the liquid and gas phases 01' a. gas mixture oi the type to the treatmeilit at which the present invention is appli. cab e,

Fig. 8 is a graph showing the variation in gross liquid recovery from such a gas mixture with pressure at various temperatures,

Fig. 4 is a graph showing the variation in net gasoline recovery from such a gas with pressure at various temperatures,

Fig. 5 is a iront elevation in diagrammatic i'orm oi an apparatus suitable for carrying out the present invention in which a dry gas and a dry condensate are delivered,

Fig. 6 is a iront elevation or a section or an in pressure cannot affect the condensation. This point is known as cricondentherm. Each of these curves A. B, C. D and E has a similar point, and a line P drawn through these points designates the pressure at which maximum liquid recovery can be had at any given temperature, and vice versa. That is to say. line P is the line oi maxiiii In Fig. l are applied suitable legends from which the nature of the method of the present invention is evident. Briefly, the method consists in conducting high p'ressure gas from a deposit or from the separator or a refinery plant, which should first be dehydrated by any conventional method or by the method hereinafter described, through a pipe I. a heat exchanger 2, and an ex.

mum gross liquid production.

Any condensation resulting from a decrease in pressure from-a point above line P is retrograde condensation. For example, assume that a mixture-exlsts at a temperature about 30' R, as

pension valve 8 into a separator l, which isv maintained at a pressure and temperature within the limits defined hereinafter. The dry gas leaves the separator through a-drawofl line 5, which is provided with a valve 6 and leads to a compressor or to any other piece oi equipment in which the gas is utilized. II it is desired to precool the feed gas, valve 6 is closed and valve 1 in a branch line 0, leading to theheat exchanger 2, is opened, whereby the cool gas passes in heat exchange relation with the incoming gas. The dry gas leaves the heat exchanger through pipe 9 which is connected to the same equipment as line 6. The liquid products recovered in separator l are drawn oi! through line l0-and conducted to a stabilizer, it necessary, or to storage tanks, or to separators and thence to storage In Fig. 2 is shown a phase diagram or a liquid recovery diagram of a gas mixture of the type, to the treatment of which the present invention is directed. In this diagram the various loops A, B, C, D, E and F represent equilibrium curves. by which is meant a curve showing the temperature and pressure through which a system containing the designated amount of liquid in gailons per thousand cubic feet oi gas can be carried without evaporation or condensation occurring. For example. any point on curve A shows the temperature and pressure which obtain when the system contains one gallon of liquid for a thousand cubic feet of gas in equilibrium. v

The diagram shown in Fig. 2 represents the phase relation of a mixture cl a plurality oi hydrocarbons of various boiling points. reason. there are a plurality oi envelopes, each designating equilibrium temperatures and pressures for a diflferent liquid content of condensate.

It will be observed that thea'mount of conden-.

sate designated by the envelopes increases in general with a decrease in temperature. It will also be observed that the rritical temperature. due to the lar e amount of methane present. is very close to the pressure art's and Ls designated by point 0. At any temperature higher thanthe critical temperature and outside of envelope F, the system is wholly in the vapor or gas phase, while at any temperature below the critical temperature and outside of the envel pe the system is wholly in the liquid phase. A line drawn from 0 to the temperature axis cuts on a sector oi the diagram to the right of this line in which retrograde action occurs. Along the curve F is a point N which indicates a temperature at which condensation cannot be eilected by an increase a gas. This point is indicated as point B. It can be seen that a reduction in pressure causes condensation, such that at 1840 pounds pressure 0.2 gallon per 1000 cubic feet will be formed, and that at 1660 pounds per square inch 0.4 gallon will be formed and that at 1300 pounds per square inch 0.6 gallon will be formed, while at 980 pounds per square inch a point 01 maximum condensation or about 0.7 gallon per 1000 cubic feet is reached. Thereafter a decrease in pressure causes vaporization, such that at about 200 pounds per For this square inch less than 0.4 gallon oi condensate will remain.

It will be understood that below line P condensation follows the conventional law and increases with pressure and decreases with temperature. It should be noted in this connection, with reference to curve B, that the same liquid recovery can be obtained at about 1220 pounds per square inch and 20' F., as can be obtained at about 240 pounds per square inch and -20" F. For practical operation according to the present invention, liquid 'recovery is eflected at temperatures between about and F. and at a pressure between about 500 and 1200 pounds persquare inch. V

It will be understood that the phase diagram shown is not intended to be a precisepicture or the phase relationships of the components or all mixtures treated according to the present invention. In fact. it is not precise with respect to the particular mixture on which it was basal That is to say that every point on the various" curves was not determined. Enough points were determined, however, to indicate that the phase diagram takes the general shape shown, and this is oilered for purposes of illustration and for a better understanding of the present invention.

In Fig. 3 is shown a family of curves which were produced by plotting pressure in pounds per square inch against gross liquid recovery in gallons per 1000 cubic feet or gas at various temperatures. It will be observed that in general the amount of gross liquid increases with the decrease in temperature. It can also be seen that the amount of recovery passes through a maximum with increase inpressure and then falls oil, indicating'that the condensation occurring at the paint of maximum recovery is retrograde condensaticn. In almost every instance the maximum gross liquid recovery occurred at a pressure above 700 pounds per square inch, although at some temperatures the amount of recovery was very close to maximum at 500 pounds 'per square inch and fell oil rapidlv from this pressure. Again. it will be noted that at 60 F. the amount of recovery fell of! rapidly after about 1200 pounds per square inch, and that this is also true at 20 and 40 F.

It will be understood that these relationships may change for'specifically d fferent mixtures,

BEST AVAILABLE COP some 3 eral relationship holds, however, for mixtures oi this pe.

In Fig. 4 is shown a family of curves obtained by plotting net gasoline, R; V. P. 20 pounds per square inch, in gallons per 1000 cubic feet against pressure in pounds per square inch, the original gas containing about 0.52 gallon per 1000 cubic leet. It will be understood that the reason tor -thelowervaluesinthisiamilyoicurvesisthat the condensate represented in the iamily curves in Fig. 3 includes normally gaseous constituents dissolved in the liquid. In this case it can be seen that-maximum net liquid recovery occurs more nearly at 500 pounds per square inch than at 700 pounds per square inch, and

that beyond 1200 pounds per square inch the recovery falls at even more sharply than was the case with gross liquid recovery. Beginning at about 40' E. 700 pounds per square inch appears to be the minimum preferred pressure (or increase in temperature.

Reierring to .Fig. 5, parts corresponding to those shown in Fig. I bear the same numerals. The apparatus shown in this figure diners from that shown in Fig. 1 by including a line for the circulation to the heat exchanger and the separator of a liquid having a greater 'aiiinity for water than oil. This liquid should be one which remains liquid at temperatures as low as those at which it is desired to operate and will boil at least as high as butane. In general. this liquid is mixed with wet gas before the latter is expanded into the separator, whereby the water in the wet gas is taken up by the liquid which settles out in the separator with the oil, with which it. or 'at least its water solution, must be immiscible. in order to be operative Suitable liquids for use in this connection are the various glycols, such as ethylene glycol, glycerol, concentrated inorganic salt solutions, and the like. Referring to the drawings, line H is provided at the bottom of the separator I for drawing on the water absorbent and conducting it back to the feed inlet I. prelerably alter compressing it by pump I! to a pressure such that it will enter line I. In practice. a certain amount oi this liquid will be periodically withdrawn and replaced by fresh liquid, or the liquid itseli' will be periodically orcontlnuously subjected to a flash distillation for separation of the liquid from water.

In Fig. 6 is shown a stabilization tower which may be used in conjunction with the apparatus shown in Fig. 1. Stabilization-tower I3 is provided with a gas drawoi! It at its upper end. and a liquid drawoil' l I at its lower end. It is also provided with a steam coil I for vaporizing undesired constituents at the pressure employed. The chief undesired constituents are propane and lower hydrocarbons. and a certain percent use of the butane which must be removed in order to reduce the vapor pressure of the gasoline to the desired amount. Line 10 from tower I of Fig. 1 passes into the top oi tower It! in' which it is formed into a coil l1, and then back out to a heat exchanger II where it is passed in heat exchange relation to the stabilized gasoline which has been heated up by the steam coil car- ,ried in line IS. The stabilized condensate is withdrawn from the heat exchanger by line is. Prior to its entry into the tower the unstable condensate is passed through an expansion valve 20 which causes expansion of this condensate in 0011 H with cnnsemmnt. nmunw nu u-msawreducing the temperature of coil ii to any desired point, and easily to the temperature required to maintain the composition of the overhead so that it contains nothing higher than butane. I

In Fig. i is shown a tower which may be substituted ior separator 4 in Fig. l, and which enables the operator to recover the dry gas which has been dissolved in the condensate from the condensate without a loss or its pressure. The tower'shown in Fig. 7 is indicated by numeral II and'is provided with a partition 22 intermediate its ends dividing it into two zones. The wet gas is introduced into the upper zone through line I and expansion valve land with the zone maintained under conditions heretofore proposed the condensate collects at the bottom thereof, while y gas passes on at the top through line I. The condensate is withdrawn through line it and passed through'heat exchanger 24 into the lower end of the bottom zone which contains a steam coil 28, which is supplied with steam at a suitable temperature ,to drive oil normally gaseous constituents of the condensate at the pressure 'maintainedin the system. The gases so driven on are withdrawn through the lower section through line 28 and passed in heat exchange relation to the liquid withdrawn from the upper zone, and are then discharged into the upper end or the upper zone to Join the dry gas leaving the system through line 5. The condensate with a reduced content oi normally gaseous constit uents, such as methane and ethane, is withdrawn irom the lower section through line 21.

In the system shown in Fig. 8 the object is to recover dry gas which has been dissolved in the condensate and at the same time stabilize the condensate without the loss in the dry gas of constituents, such as propane and butane, which may be desired for some other purpose. In this system the rich gas is introduced through line 28 into a heat exchanger 29 where it gives up heat to the condensate initially produced, and is then passed through a second heat exchanger 30 where it gives up heat to the dry gas initially produced, and .then passes through expansion valve Ii into the separator II. The condensate is withdrawn .trom the separator-through line it and passed to heat exchanger 15, while dry gas is withdrawn from the separator through line I and passed through heat exchanger 30. and then to a second heat exchanger 81 hereinafter referred to. Separator is provided atits upper end with a cooling coil 38 which need not be usedii suiiicient temperature reduction can be secured by expansion oi the wet gas.

The condensate leaving tower 34 contains some dry-gas dissolved therein. and this condensate is heated up in heat exchanger 29 and then passes through line 82 to a dash drum 39 from the upper end of which the dry gas passes oil through line 40. This dry gas inevitably carries 01! some desirable constituents with it. so it is added to Btabilized liquid is withdrawn from the bottom oi stabilizer it through line ll. and is conducted to a heat exchanger 42,- where it im its heat to the incoming condensate. Line II is provided with a bypass containing a pump ll, while line it is provided with a bypass ll containing a compressor ll. Since it isdesirable to have the dry as from the whole system at the pressure maintained in separator ll. it is necessa ry either to compress the condensate from flash drum II and to operate the stabilizer II at this pressure, or to compress the overhead from the stabilizer. The former is generally the more economical procedure.

In order to impart flexibility to the system, line I2 is provided with a bypass II in which is a pump It, and line It is provided with a bypass I! in which is a compressor it. Thus separator It may be operated at iairly low pressures. and the gases resulting therefrom are compressed in compressor It. and the liquids pumped by pump it into stabilizer I. Alternatively. stabilizer ll can also be operated at low pressure andthe gases resulting thereirom compressed by compressor Ii. Or by the use or pump ll, the separator I! may be operated at relatively high pressure 'and the stabilizer 48 at relatively low pressure.

ascanbeseemthesystemillustratedinrig. 8 utilises to the fullest extent the energy contained in the various components or the initial mixture, and yields a stabilized gasoline and a dry'gas at a high pressure which may be used for reprmsuring producing formations or for any other purpose where high Pressure gas is desired. It will be understood that the drying arrangement shown in Fig. 5 is applicable to the apparatus shown in Fig. 8 as well as to the apparatus shown in the other figures. Likewise, .the condensate line in Fig. 8. instead or going to the first heat exchanger. can go to.the stabilizing tower as shown in Fig. 6.

From the above description, it will be apparent that the present invention relates to the recovery of condensable constituents irom high them, the recovery to of at least 500 pounds been shown, the operpressure gases containing be eiiected at a pressure per square inch. As has 'ation is preferably conducted at a pressure or at least 700 pounds per square inch and may be conducted at pressures as high as 1200 pounds per square inch, provided the initial wet gas is available at pressures substantially in excess or 1200 pounds per square inch, such as 2000 pounds per square inch which is quite common in many fields. The separator may be maintained at any convenient temperature or between about -50 and +60 F., the lower temperatures in this case being rather cheaply attained, when the wet gas is at a sufiiciently high pressure, by expansion oi the gas to the separation pressure with suitable heat exchange.

In the apended drawings apparatus has been shown in which the high pressure gas is expanded in the separator so'that the desired.tempcrature in the separator can be attained. In some cases the initial gas is not at sumciently high pressure to produce the desired low temperature merely by expansion to the operating pressure. In this case it will be evident that the temperature oi the separator may be maintained by extraneous refrigeraiton, such as by the employment of cooling cofls such as shown in Fig. 8.

The method. as practiced in the various types of apparatus shown in the drawings. consists in came M1118 a 888. containin nnrmnliv "mm-t nan-H6. 7s

.stanti lly and separating the resulting condensed constituingthepressureonthegastobringittothede-.

sired separation pressure and temperature.

It will be apparent that the apparatus shown in the various figures is merely illustrative and may be changed substantially without departing from the scope oi the present invention. Mention may be made of the fact that all oi the low temperature vessels should be encased with a heavy ssingsoastoconserve energyto thegreatest The nature and objects oi the present invention having been thus described and illustrated. whatisclaimedasnewanduseiulandisdesired tobesecuredbyLettersPatentis:

1. The method or recovering desirable liquefiable constituents from natural gas which is iniially at a high pressure within the retrograde condensation comprises, precooling'said gas while undersaid high pressure to a temperature below its initial temperature. but above the final desired temperature or condensation of said constituents, then reducing said high pressure substantially only within the retrograde condensation range of said constituents at said final temperature and thereby to further cool said gas to said final temperature. and separating the resulting condensed constituents i'rom uncondensed gas.

2. The method of recovering desirable liquefiable constituents from natural gas which is initially at a high prmsure within the retrograde condensation range or said constituents which comprises, cooling said gas below its initial temperature while said gas is maintained under said high pressure. thereafter reducing said high pressure suillcientiy only to produce retrograde condensation or said constituents at the reduced temperature, separating the resulting condensed constituents irom uncondensed gas. and utilizing the refrigeration eiiect produced in the gas by the reduction in pressure to accomplish the aforesaid 8. The method oi. recovering desirable liquefiable constituents irom natural gas which is initially at a pressure above 700 pounds per square inch which-comprises, cooling said gas while under said pressure to a temperature below its initial temperature but above the final desired temperature, then reducing said initial pressure subonLv within th retrograde condensation range of said further cool said gas to said final temperature,

cuts from uncondensed gas.

4. The method of recovering desirable liquefiable constituents from gas which is initially at a high pressure within the retrograde condensation range of said constituents which comprises, cooling said gas in a series of cooling stages of progressively decreasing temperature to a final temperature suitable to condense said constituents. reducing said pressure only in the final one oi said cooling stages and suiilciently only to produce retrograde condensation of said constitue ents and to cool said gas by the expansion thereof to said final temperature, separating condensed constituents rrom uncondensed gas in said final cooling stage. and utilizing saiduncondeused gas as a cooling medium in an earlier one oi said cooling stages.

5."l'he of recovering desirable liquefirange or said constituents which tially at a high Pressure within the ram condensation range or said constituentl which comprises, cooling said gas sufliciently to condense said constituents while the an is mantained under said high pressure, thereette reducing said high pressure substan ially only within the retrograde condensation range of aid eon- 5 Blidfllhll'll :upriortathereductioninpressure thereof.

BI'UART E. BUCKLEY. 

